Lithium Transport Simulations in Glassy Zwitterionic Electrolytes Show No Superionic Conductivity

Decoupling of lithium-ion motion from structural rearrangements of the electrolyte characterizes superionic conductivity, which is highly sought after for applications in lithium batteries. While superionic conduction is well established in ceramic electrolytes, evidence of superionic conduction in polymers has been limited to only a few studies. We use molecular dynamics simulations to investigate the correlation of ionic conductivity with molecular rearrangements in polymerized and small-molecule zwitterionic electrolytes. We use a combination of virtual sites and coarse-graining to overcome the slow dynamics of charged polymers while preserving the structural details of the molecules. We estimate the time scale for molecular rearrangements from the diffusion of zwitterions in the electrolyte. We find that the ionic conductivity scales with molecular rearrangements of the electrolyte, with no evidence for decoupling of lithium motion.